The present invention relates generally to printing presses and, more particularly, is directed to a metering roll system for a lithographic offset printing press.
Printing presses, such as lithographic offset presses, for printing commercial quality brochures, magazines and the like are well known in the art. For example, a web-fed lithographic offset press sold by Hantscho, Inc. of Mount Vernon, NY under the trademark "MARK 10" is of such type. These presses include a plurality of printing units, each having an ink fountain which provides the color for one of the plates used in the printing operation.
Specifically, a printing press can generally print one or more webs or rolls of paper at one time. For each web to be printed, upper and lower ink fountains are provided which supply ink to respective printing plates. Since only three basic colors, that is, magenta, cyan and yellow, are necessary to produce all other colors, only four different color ink fountains need be provided, black being the fourth color. Since each web is printed on both sides, four plates (and four ink fountains) are provided in series on the upper side of each web, and four plates (and four ink fountains) are provided in series on the lower side of each web. The eight plates constitute a form, that is, the number of plates used to print a signature.
Each ink fountain includes an ink fountain roll associated with one plate, and which supplies ink to the respective plate through a metering roll and a series of intermediate rolls. The intermediate rolls may include, in series, a first distribution roll, a driven distribution roll, a second distribution roll, an ink vibrator roll, and an ink form roll, between the metering roll and the plate to be supplied with ink.
The metering roll, the first distribution roll and the driven distribution roll are rotatably mounted on axles, with the ends of the axles terminating in side brackets. The side brackets, in turn, are pivotally secured to the machine frame at a point just above the axle for the driven distribution roll, whereby the entire assembly of the metering roll, distribution roll and driven distribution roll, can be pivoted by throw-off mechanisms, to move the metering roll away from the fountain roll, for example, when it is desired to run the press in the idle mode with no ink.
It is important that a proper gap be maintained between the fountain roll and metering roll at all times, so that the proper amount of ink is transferred to the plate. In this regard, conventional systems include a paralleling adjustment on the throw-off mechanisms to insure that the metering roll is parallel to the fountain roll. Such systems further include fixed stops associated with the metering roll, and particularly, in contact with the side brackets, to adjust the gap, which may be, for example, 0.003 inches.
In order to set the gap along the entire length of the metering roll, the throw-off mechanisms are turned ON to position the metering roll adjacent the fountain roll. Then, both fixed stops on either side are backed off to permit a paralleling operation. Specifically, the paralleling adjustments on the throw-off mechanisms are adjusted to provide that the metering roll is parallel to the fountain roll and that there is a positive interference or contact of the metering roll with the fountain roll, along the entire length of the metering roll. The two fixed stops are then adjusted to adjust the metering roll and thereby provide a uniform gap of approximately 0.003 inch along the entire length of the metering roll. The stops are then checked to make sure that they are in contact with the side brackets, and that the throw-off mechanisms operates properly.
However, such system requires time consuming and complicated operation set-ups. Further, with such system, after operation for a period of time, further adjustments may be required to insure that the gap is maintained constant. Still further, since the separation between the fountain roll and the metering roll are constant, if there are any eccentricities in the rotations of the fountain roll or metering roll, due to, for example, the respective axles being offset from the central axes thereof, the gap will change, during rotation of the metering roll and fountain roll. This necessarily changes the transfer rate of ink required for the printing process.